Polymethylmethacrylate (PMMA) bone cements are based on the pioneering work of Sir Charnley. PMMA bone cements consist of a liquid monomer component and a powder component. The monomer component generally contains the monomer, methylmethacrylate, and an activator (N,N-dimethyl-p-toluidine) dissolved therein. The powder component, which is also referred to as bone cement powder, comprises one or more polymers, a radiopaquer, and the initiator dibenzoylperoxide. The polymers of the powder component are produced on the basis of methylmethacrylate and comonomers, such as styrene, methylacrylate or similar monomers by means of polymerisation, preferably by suspension polymerisation. During the mixing of powder component and monomer component, swelling of the polymers of the powder component in the methylmethacrylate generates a dough that can be shaped plastically and is the actual bone cement. During the mixing of powder component and monomer component, the activator, N,N-dimethyl-p-toluidine, reacts with dibenzoylperoxide while forming radicals. The radicals thus formed trigger the radical polymerisation of the methylmethacrylate. Upon advancing polymerisation of the methylmethacrylate, the viscosity of the cement dough increases until the cement dough solidifies.
PMMA bone cements can be mixed by mixing the cement powder and the monomer liquid in suitable mixing beakers with the aid of spatulas. One disadvantage of said procedure is that air inclusions may be present in the cement dough thus formed and can cause destabilisation of the bone cement later on. For this reason, it is preferred to mix bone cement powder and monomer liquid in vacuum mixing systems, since mixing in a vacuum removes air inclusions from the cement dough to a large extent and thus achieves optimal cement quality. Bone cements mixed in a vacuum have clearly reduced porosity and thus show improved mechanical properties. A large number of vacuum cementing systems have been disclosed of which the following shall be listed for exemplary purposes: U.S. Pat. Nos. 6,033,105 A, 5,624,184 A, 4,671,263 A, 4,973,168 A, 5,100,241 A, WO 99/67015 A1, EP 1 020 167 A2, U.S. Pat. No. 5,586,821 A, EP 1 016 452 A2, DE 36 40 279 A1, WO 94/26403 A1, EP 1 005 901 A2, U.S. Pat. No. 5,344,232 A.
Cementing systems, in which both the cement powder and the monomer liquid are already packed in separate compartments of the mixing systems and are mixed with each other in the cementing system only right before application of the cement, are a development of cementing technology. Said full-prepacked mixing systems were proposed through EP 0 692 229 A1, DE 10 2009 031 178 B3, U.S. Pat. Nos. 5,997,544 A, 6,709,149 B1, DE 698 12 726 T2, and U.S. Pat. No. 5,588,745 A.
Patent DE 10 2009 031 178 B3 discloses a closed vacuum mixing system having a two-part dispensing plunger for closure of a cement cartridge. A combination of a gas-permeable sterilisation plunger and a gas-impermeable sealing plunger is used in this context. This principle of a closed vacuum mixing system is implemented in the closed cementing system, PALACOS® PRO, made and distributed by Heraeus Medical GmbH.
In conventional vacuum mixing systems, the monomer liquid container is opened either by manual twisting of the ampoule head, such as is proposed, for example, in WO 2010/012114 A1, or by manual puncturing of monomer liquid pouches. Subsequently, the cement powder is mixed with the monomer liquid by means of manually operated mixing devices. It is expected that there will be a need for maximally simplified vacuum mixing systems in the future. These should be autonomous and work largely automatically to the extent possible.
Accordingly, it is the object of the invention to overcome the disadvantages of the prior art. Specifically, the invention is to provide an opening device for a monomer liquid container, a vacuum mixing system, and a method to the opening of a monomer liquid container, all of which enabling strongly simplified application. In this context, the monomer liquid container is to be opened within a closed system and/or a closed or closable vacuum mixing system without parts of droplets of the content possibly being released to the outside.
Accordingly, one object of the invention is to develop a device for the non-manual opening of monomer liquid containers. This means that the device, after activation, is to provide for a safe autonomous opening of the monomer liquid container. The drive of the device must not be driven by external energy sources in this context. The aim is to use a simple and storable energy source that can be integrated into a closed vacuum mixing system.
Moreover, a closed vacuum mixing system that has the opening device for the opening of the monomer liquid container integrated into it is to be developed. The vacuum mixing system is to contain a cement cartridge, in which a cement powder is stored, as well as a separate monomer liquid container, in which the monomer liquid is situated. Accordingly, the monomer liquid is stored separate from the cement powder. Any contact of the medical users with said components shall be excluded before and after the mixing of the two cement components—i.e. the cement powder and the monomer liquid. Therefore, the monomer liquid container shall be opened and the monomer liquid shall be transferred in a closed system. The cement powder must not contact the medical user either.